Feature Description

The Monitor Subscriber (MonSub) feature enables tracing of subscriber-related information which includes user and control traffic, and events such as charging and internal events that are useful for debugging. By default, this information is displayed on the Control Plane console, where you can execute MonSub tracing CLI command, and captured in a Packet Capture (PCAP) file on the User Plane.

User traffic is carried on slowpath where packets traverse to the application or fastpath where packets do not have to traverse up to the application but are offloaded to fastpath processing (VPP). Slowpath mode was the default mode until fastpath offload (VPP) into SAEGW, was introduced.

Monitor Subscriber provides the following functionality:

  • Continuous capture of user traffic from fastpath in PCAP files on the User Plane.

  • The non-user traffic information, that is, control event traffic and other related information are displayed in Control Plane console and are captured in separate PCAP files on the User Plane.

  • New option UP PCAP trace [W - UP PCAP Trace (ON)] is introduced for CUPS on Control Plane and User Plane in MonSub CLI. The new option is like the D option in the ICUPS. The slow-path and fast-path PCAP generates only when this option is ON.

  • There are a maximum of four subscriber tracing sessions per NPUMGR instance. The NPUMGR (per User Plane instance) enforces the maximum tracing session limit. Slow-path capture naming convention contains the MonSub tracing session ID on SMGR instance, whereas fast-path tracing session contains the PSN as session ID. If there are already four tracing sessions running at SESSMGR instance, then slow-path capture is by name “S4”. It continues until the time NPUMGR rejects the tracing session due to max tracing limit reached.

Following are some of the important definitions that are related to this feature:

  • Chassis Traffic Volume: The total volume of packet throughput on the chassis.

  • Monitored Traffic Volume: Monitoring of the total throughput of all the subscribers through MonSub across all the MonSub sessions.

  • PCAP success: The percentage of the MonSub traffic capture request and the successful capture in the PCAP files.

Packet Processing Throughput

Following are the scenarios that impact the packet processing throughput:

  • When VPP utilization is above 80%, MonSub may have an impact to packet processing throughput. The impact is in proportion to the monitored traffic volume.

  • Specifically, when the monitored traffic volume approaches 10% of the chassis traffic volume, there may be an impact on the VPP throughput causing subscriber packet loss.

  • The impact to packet processing throughput is higher when using monitor priorities above 0 (zero).

    Caution

    You must be cautious during the packet processing. When VPP is running at 80% utilization and handling approximately 10-Gbps chassis traffic volume, there’s an impact on the packet processing, if the set of MonSub sessions is collectively monitoring the subscribers, totaling more than 1 Gbps of monitored traffic volume.

PCAP Success

The PCAP success depends on the following factors:

  • The level of PCAP success depends on several factors, including monitored traffic volume, VPP utilization, MonSub monitor priority, and background disk I/O.

  • In general, the PCAP success rates are greater for the following cases:

    • When the VPP utilization is low and/or MonSub monitor priority is above best-effort.

    • When the monitored traffic volume is less than 10% of the chassis traffic volume.

    Example: When VPP is running at 80% utilization, handling approximately 10-Gbps chassis traffic volume, monitored traffic volume up to 1 Gbps is likely to yield high PCAP success percentages.